The present invention relates to a method and a device for controlling the slippage of a vehicle wheel.
A method and a device for controlling the slippage of a vehicle wheel are described in German Patent No. 44 30 108. The wheel-slip control system described in German Patent No. 44 30 108 reduces the drive torque of a drive unit of the vehicle by a predefined amount in response to incipient slippage at least at one of the driven wheels. In the determination of the magnitude of the drive torque reduction, in addition to the coefficient of friction, the driving situation, for example, whether the vehicle is driving straight ahead, cornering, or entering a curve, is taken into account. In this context, the magnitude of the drive torque reduction is selected such that, given a constant coefficient of friction, the magnitude of the reduction is smallest during straight-ahead driving and greatest during cornering, whereas the magnitude of the reduction lies between these two magnitudes while entering a curve. Moreover, the lower the coefficient of friction, the greater the drive torque reduction is selected to be. By these measures, the stability of the vehicle is improved as a function of the curve condition, as well as while entering a curve, and during cornering. In this context, only the magnitude of the drive torque reduction is emphasized while the response characteristic of the traction controller is independent of the driving situation.
An object of the present invention is to specify measures by which a wheel-slip controller is adapted to different driving situations.
By recognizing a curve exit and making allowance for it during the control, it is made possible for the slip controller to be influenced in the direction of improved traction during curve exiting. In this manner, a traction gap on the curve exit felt unpleasantly by the driver is effectively prevented. The vehicle behavior during an entire cornering event is improved since the controller is optimized for stability during curve entry and during cornering while being optimized for improved traction during curve exiting.
It is particularly advantageous for the controller to be influenced by varying the slip thresholds. The slip thresholds, for improving the stability, are markedly reduced at the curve entry compared to the slip thresholds during straight-ahead driving; increased during cornering; and further increased during curve exiting in the direction of the slip thresholds during straight-ahead driving. Thus, in the curve section endangering the stability, a more sensitive response characteristic is ensured that improves the vehicle""s stability.
If, additionally, the drive torque of the drive unit is influenced as a function of the a curve condition, a harmonic control response is achieved over the whole curve range, and stability and traction are optimized. It is a particular advantage that, besides or in lieu of the threshold variation, the drive torque control is modulated as a function of the curve area. In this context, the correction steps for the drive torque (in the reducing or increasing direction) and/or the controller dynamics are influenced as a function of curve entry or curve exit, for example, by making the reducing torque correction steps greater and the reduction faster on the curve entry while the increase in torque is slower and the steps smaller, respectively, whereas on the curve exit, the reduction is slower, the size of the correction steps is smaller and, during the increase in torque, the steps are greater and, consequently, the engine torque is increased faster.